1. Field of the Invention
The invention relates to an arrangement for the mechanical coupling of physical units, such as, for example, of a printing assembly of an electrophotographic printer or of a copier, to further physical units in axially parallel orientation with respect to the transport path of a recording carrier running through.
2. Description of the Related Art
Printers or copiers working on the electrophotographic principle are generally known. The electrophotographic printing principle as such involves a relatively high outlay. As an intermediate carrier for printing information generally there is provided a continuously rotating photoconductive drum which is initially charged uniformly when rotating in order to generate a latent charge image. The uniform charge is discharged light-optically point-by-point as a function of the printing information and consequently produces on the intermediate carrier a charge distribution corresponding to the printing information. This charge image is inked by means of a toner mixture by the utilization of electrostatic forces, and subsequently the toner particles are transferred onto a recording carrier and fixed there chemically or thermally.
Especially critical junctures in this process are the transfer of the toner particles onto the recording carrier, the so-called transfer printing, the further transport of the recording carrier together with the transfer-printed toner image which is not yet smudge-proof, and the fixing operation. Particularly in this region of the transport path of the recording carrier through the printer or copier, the quality of the printing result is influenced decisively. Thus, for example, it is of paramount importance that, in the transfer-printing station, the recording carrier be moved exactly axially parallel to and without relative speed in respect of the intermediate carrier, that is to say the photoconductive drum, otherwise the printing image is smudged even as early as here. The fixing operation is similarly critical, especially when the fixing of the toner image on the recording carrier is executed by means of the thermal printing process. In this process, the recording carrier runs between a pair of rollers, the so-called fixing roller and the pressure roller. The heated fixing roller, which faces toward the image side of the recording carrier, transmits a sufficient quantity of heat to the recording carrier in order, in combination with the pressure exerted by the pressure roller, to plasticize the toner particles and fuse them on the surface of the recording carrier. Here too, it is of absolutely essential importance that said pair of rollers at the fixing station be set exactly axially parallel to the transport path of the recording carrier, otherwise there are not only mechanical pinchings of the conveyed recording carrier, but also defects in the fixing which lead to a reduction of the printing quality.
It must be remembered, at the same time, that current electrophotographic printers generating the printing information in the form of dots by the screen process already produce in the high-performance range a screen of the order of magnitude of 600 dpi (dots per inch) and more. Screen-dot widths of the order of magnitude of 0.04 mm and below correspond to this. These figures highlight the mechanical and structural requirements demanded as regards the accuracy of transport of the recording carrier with respect to the individual assemblies of the electrophotographic printer or copier, if the aim is to obtain a printing result having the contrast definition which can be achieved per se by means of the printing process.
Known furthermore is the basic mechanical construction of such printers or copies which work on the electrophotographic principle. In addition to the exact allocation of individual assemblies of the printer or copier to the transport path of the recording carrier obtained by means of drive and guide elements, it is necessary, moreover, to bear in mind that individual assemblies should be relatively easily accessible, for example for maintenance work. Finally, at least some of these assemblies should also be pivotable away from the transport path of the recording carrier. This is especially true when the recording carrier is fashioned as continuous stock and, before the start of a printing operation, the start of a paper web first has to be inserted into the printer or copier.
The mechanism of electrophotographic printers or copiers is correspondingly complicated and involves a high outlay. For simpler mounting, but also for maintenance reasons, therefore, electrophotographic printers or copiers are constructed in a modular manner from individual physical units, appropriate tolerance limits being adhered to within a module, so that this module can then also be exchanged in a relatively simple way, apart from a secondary condition, namely that, after such an exchange, the necessary axially parallel orientation with respect to the corresponding part of the transport path of the recording carrier has to be provided once again. The first mounting in the assembling of the individual physical units to form a printer or copier therefore conventionally necessitates a series of time-consuming measures involving a high mechanical outlay, precisely also in order to orient all the individual physical units exactly axially parallel to one another. The same applies accordingly when test or maintenance work has to be carried out.